Chitin is a natural polysaccharide present in various marine and terrestrial organisms, including crustacea, insects, mollusks, and microorganisms, such as fungi. The structure of chitin is that of an unbranched polymer of 2-acetoamido-2-deoxy-D-glucose (N-acetyl-D-glucosamine), and can be represented by the general repeating structure:

Chitin is typically an amorphous solid that is largely insoluble in water, dilute acids, and alkali. Although chitin has various commercial applications, greater commercial utility is found by converting chitin to the deacetylated product chitosan. Chitosan can be created by N-deacetylation of the chitin polymer, and its structure may be represented by the following general formula, wherein at least some of the acetylamine groups have been converted to amine groups:
Chitosan is also an amorphous solid that is largely insoluble in water, but is soluble in aqueous organic acids, such as formic and acetic acids. However, the deacetylation reaction is typically not complete, and some of the acetyl groups remain in most chitosan compositions. In the representation above, all of the formerly acetylated amine groups have been converted to amine groups.
Chitosan has many industrial, medical, pharmaceutical, and nutritional uses, including those requiring a biodegradable, non-toxic polymer. For example, chitosan is used as a polyelectrolytic coagulant and a sludge dewatering aid in wastewater treatment. Medical, pharmaceutical, and nutritional uses often require a higher quality chitosan for functional and aesthetic reasons. These uses include applications as anticoagulants, antiviral agents, drug carriers, cosmetic additives, dialysis membranes, orthopedic materials, wound dressings, food stabilizers and thickeners, flavor and nutrient carriers, and dietary fiber.
The quality of chitosan varies with the degree of substitution of the N-acetyl groups, degree of polymerization, manufacturing process, color, clarity, consistency, uniformity, and source. Most chitosan is formed by dissolving calcium carbonate from the shells of aquatic crustacea to liberate chitin, deacetylating the chitin to form chitosan, followed by recovery and drying of the chitosan. One problem with recovery from crustacea is that it is very difficult to obtain uniform, high quality chitosan. The uniformity problems occur in part because the crustacea typically are varying sizes, ages, and species; grow under varied environmental conditions; and are gathered from different locations. The quality issues arise in part due to the fact that sufficiently uniform chitosan cannot be obtained, but also include the fact that chitosan obtained from crustacea often has high ash content and can contain heavy metals that is concentrated in the crustacea from their aquatic environment. A further problem with chitosan derived from harvested crustacea is that it has the potential to include undesired proteins and allergens.
Other methods of producing chitosan involve recovery from microbial biomass, such as the method taught by U.S. Pat. No. 4,806,474. Unfortunately, existing methods of recovering chitosan from microbial biomass need improvement to produce higher quality chitosan that is more suited for pharmaceutical, nutritional and cosmetic applications. For example, a need exists for chitosan having improved consistency and solubility, as well as higher levels of deacetylation than is currently practiced. Present processes do not allow for sufficiently high levels of deacetylation while also providing high quality chitosan from a consistent and controlled raw material source. For example, deacetylation levels of less than 75 percent can be obtained by methods taught in U.S. Pat. No. 4,806,474 to Herschberger, but even higher deacetylation levels are desired. When these higher deacetylation levels are obtained, it is also desirable that other properties of the chitosan be retained or improved. Another method, taught by U.S. Pat. No. 4,282,351, teaches only how to create a chitosan-beta-glucan complex.
Therefore, a need exists for an improved chitosan material that is obtained utilizing an improved method.